Two dimensional X-ray detectors are finding increasing use in diffraction studies of biological macromolecules, especially with the advent of high intensity x-ray sources and computer aided analysis systems. Currently available detectors all suffer from performance limitations, maintenance requirements and/or exorbitant costs. The proposed research is aimed at the development of a large area single crystal detector with excellent quantum efficiency, no image distortion and high maximum data rates. The technology to be used is based on the large area silicon avalanche photo diode developed at Radiation Monitoring Devices, Inc. for nuclear counting applications and should result in a reliable detector with reasonable costs. Phase I research will be directed at investigating the feasibility of spatially resolved charge collection from both sides of the device and at optimizing the quantum efficiency in the x-ray region. During Phase II we hope to use these techniques to develop a large area array detector for eventual production and sale to the molecular biology research community.